How are hormonal effects on sexual behavior mediated at the level of individual neurons or neural circuits? As logical steps toward answering this question, the proposed research aims to achieve: 1) a description of the neural circuitry controlling female mating behavior in the golden hamster (Mesocricetus auratus), and 2) analysis of functions of particular parts of the circuitry. The research will focus on the role of the hypothalamus and its connections in mediating sexual receptivity. We have shown that lesions in the region of the ventromedial nucleus of the hypothalamus (VMN) can reduce or eliminate sexual receptivity in ovariectomized, hormone-primed females. Our recent work using hypothalamic knife cuts indicates that the antero-lateral, and not the posterior or postero-lateral connections of this region are critical for this behavior. The technique of horseradish peroxidase (HRP) histochemistry will be used to describe hypothalamic connections in the hamster and to help to determine which of these are important for sexual receptivity. In other experiments, estrogen and progesterone will be implanted in the brain to determine their sites of action for inducing receptivity. In summary, the experiments proposed will attempt to further define the neural pathway or pathways that mediate the effects of gonadal steroids on female mating behavior.